1. Field of the Invention
The present invention relates to an electronic device, such as a camera, powered by a fuel cell and a power supply system for the same which uses a fuel cell.
2. Description of the Related Art
As disclosed in Japanese Patent Laid-Open No. 9-213359 (corresponding to U.S. Pat. No. 6,057,051), a known fuel cell apparatus includes a fuel cell body that generates electricity, a fuel tank for storing fuel to be supplied to the fuel cell body, a fuel supply unit, an air supply fan, and a control unit that controls power generation of the fuel cell body. These components are housed in a case, as a unit. The fuel cell apparatus is housed in a fuel cell chamber provided in an electronic device, for example, a computer.
The basic configuration of a commonly used fuel cell will be described with reference to FIGS. 6A and 6B. FIG. 6A is a plan view of a fuel cell, and FIG. 6B is a front view thereof.
This fuel cell has vents 73 for taking in air including oxygen used as an oxidizer for reaction. The vents 73 are provided in the top, bottom, front, and back surfaces of a case 70. The vents 73 are also responsible for discharging generated water in the form of vapor and for exhausting heat generated by the reaction. Electrodes 72 for outputting electricity are provided in a side surface of the case 70.
The case 70 houses generating cells 71, a fuel tank 76, a fuel supply path 75, and a pressure sensor 77. Each fuel cell 71 includes a fuel electrode 113, a polyelectrolyte membrane 112, an oxidizer electrode 111, and a catalyst. The fuel supply path 75 connects the fuel tank 76 with the fuel electrode 113 of each generating cell 71. The pressure sensor 77 measures the pressure of fuel.
The fuel (for example, hydrogen) stored in the fuel tank 76 is supplied to the fuel electrode 113 through the fuel supply path 75. The oxidizer electrode 111 is supplied with air through the vents 73. The electricity generated in the generating cells 71 is supplied to an electronic device through the electrodes 72.
There is proposed a technique that makes it possible to use portable electronic devices (for example, a notebook computer, camera, and camcorder) for long hours by providing the above-described fuel cell in the portable electronic devices. In Japanese Patent Laid-Open No. 2003-344919, there is proposed a technique for stably supplying power to an electronic device (digital camera) despite rapid change in the power consumption, by controlling the current supply from a fuel cell to two secondary cells depending on whether the power is ON or OFF, modes of the digital camera, and remaining capacity of the secondary cell serving as a main power source. In addition, there is proposed a technique for preventing deterioration of generating cells of a fuel-cell apparatus by controlling fuel supply to the fuel cells.
The above-described known fuel-cell apparatus temporarily stores electric power generated using a generating cell before supplying. That is to say, the fuel-cell apparatus generates electricity using a generating cell, and then converts the power appropriately for control of the electronic device. Therefore, the cell has a relatively large generation capacity according to the maximum power consumption of the electronic device, and the cell is always filled with fuel, so that the maximum output can always be obtained.
However, electronic devices such as a camera include circuits that consume a small power and circuits that consume a large power. For example, in a standby mode in which the electronic device maintains only display function, power consumption is small, and therefore the maximum output of the generating cell is not necessary.
In other words, in the electronic device including circuits or controls having different power consumption, the generating cell is always filled with fuel and always performs power generation at maximum output even when a small amount of power is enough. Since power generation (fuel supply) is not performed appropriately for characteristics of the circuits or the controls, processing and control depending on circuits are needed. This complicates the configuration of circuits.
If the cell is filled with fuel for long hours, the fuel in contact with the medium is consumed. In addition, the cell deteriorates, and consequently generating efficiency deteriorates. Due to deterioration of the generating cell, the user needs to replace the cell frequently. In the case where a fuel-cell apparatus has only a single cell, the user needs to replace the entire cell. This increases the burden on the user.
In the above-described fuel-cell apparatus of Japanese Patent Laid-Open No. 2003-344919, fuel is supplied to a plurality of cells. However, the remaining amount of fuel in each cell needs to be checked individually. This complicates the control of fuel supply.